1) Site drainage
2) Powdery Mildew
I have posted in the past how it seemed very odd that vines in the same row show very mixed growth patterns as well some varieties in general that seem to lag way behind - like Baltica which budded early than any other variety. Well there might be a very plausible reason. The weather has been very hot and dry since early July and while the vines look very healthy above ground there may be a water issue below ground.
|Dried ground indicating lack of water in certain areas |
corresponding with slower vine growth
I mowed the vineyard earlier on in the week and noticed that in some areas the weeds/grass was quite thick and green, but in other areas (on the same row) it was very sparse and even dry brown. On further inspection, where many of the dry brown areas occurred in the vineyard, it corresponded quite closely with the poor vine growth - a narrow band down the middle starting at the top (whites) and getting more widespread near the bottom (reds).
|Dried areas through the row between rows 19-20. Vines here|
show less vigor then in other areas.
Our initial tests showed and good layer of sandy loam in the 4 test pits we dug with a more coarse sand layer occurring around the 65 to 70cm mark in all locations. It seems with the middle of the plot there may be a much shallower sand layer and these areas could be suffering from lack of water, stunting the vine growth. At the bottom area, around the lower 4 or 5 rows, it is essentially the whole row that is showing dried brown grass, indicating a lack of water.
This will need some more observation as the vines themselves do not look too stressed from lack of water so it is too soon to say this is the only reason for some slow growth, but it definitely could be a contributing factor.
Powdery mildew (PM), also known as oidium, is caused by the fungus Uncinula necator. This fungus has a narrow host range attacking mainly grape plants and a few related species. I will not go into all the details of what PM is and the damage it can cause as Google can do it better then I can, but for vineyards it is a very common occurrence particularly in wetter climates like ours. Kumulus spray (organic sulfur) is the spray of choice and we have been able to spray our vineyard 4 times this years - not enough it seems as we have some vines that are affected. We currently use a backpack sprayer, which is fairly inefficient and does not have the pressure to penetrate all the foliage that well.
I think our infection is early and not many leaves were identified with PM, mainly there was evidence of discoloration and splotches on the canes.
|Early signs of powdery mildew on Ortega canes|
We tried to select as many varieties as we could that were more resistant to PM but our weather has been ideal for PM so it hard to combat. This is less of a concern for us this year as we are not allowing our vines to fruit, but in coming years, controlling PM is essentially as it will rot the fruit rendering it unsuitable to wine.
Affected varieties included some that are reported to be less susceptible to PM like Auxerrois and the Blatnners so very few were missed.
Whites: Siegerebbe, Ortega, Auxerrois, Mad Angie and Mad Sylvaner, Petit Milo, Epicure, 48-05-49
Reds: LaBelle, Zweigelt, Baltica
Another spray in 7 to 10 days should aid in control and prevent PM from spreading to unaffected vines. Our hope is to secure a more efficient means of spraying for next year, so our sprays will be easier and more efficient and prevent further outbreaks.
As always, I welcome any comments of questions,